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The ras-related protein Ral is monoglucosylated by Clostridium sordellii lethal toxin
1Institut für Pharmakologie and Toxikologie, Albert-Ludwigs-Universität Freiburg, Germany.
Abstract:
Clostridium sordellii lethal toxin (LT), a cytotoxin which causes preferential destruction of the actin cytoskeleton, has been recently identified as glucosyltransferase to modify the low molecular mass GTPases Rac, Ras and Rap. We report here on LT produced by C. sordellii strain 6018 which glucosylates in addition to Rac, Ras and Rap the Ral protein. LT from strain VPI9048 however does not glucosylate Ral. Besides recombinant Ral, cellular Ral is also substrate. In the GDP-bound form, Ral is a superior substrate to the GTP form. Acceptor amino acid for glucose is threonine-46 which is equivalent to threonine-35 in H-Ras located in the effector region. The Ral-glucosylating toxin is a novel isoform of Ras-modifying clostridial cytotoxins.
Insights
Clostridium sordellii lethal toxin (LT) modifies Ral proteins, a novel finding. This cytotoxin targets the actin cytoskeleton by altering GTPases, impacting cellular functions.
Area of Science:
- Microbiology
- Molecular Biology
- Toxicology
Background:
- Clostridium sordellii lethal toxin (LT) is a cytotoxin known to disrupt the actin cytoskeleton.
- LT functions as a glucosyltransferase, modifying low molecular mass GTPases like Rac, Ras, and Rap.
Purpose of the Study:
- To investigate the substrate specificity of LT from different C. sordellii strains.
- To identify novel targets of LT beyond Rac, Ras, and Rap.
Main Methods:
- Expression and purification of recombinant LT from C. sordellii strains 6018 and VPI9048.
- In vitro glucosyltransferase assays using recombinant Ral protein and cellular extracts.
- Site-directed mutagenesis to identify the glucose acceptor amino acid.
Main Results:
- LT from C. sordellii strain 6018 glucosylates the Ral protein, in addition to Rac, Ras, and Rap.
- LT from strain VPI9048 does not exhibit Ral-modifying activity.
- Ral in its GDP-bound form is a preferred substrate over its GTP-bound form.
- Threonine-46 of Ral is identified as the specific amino acid residue modified by glucose.
Conclusions:
- A novel isoform of Ras-modifying clostridial cytotoxins capable of Ral-glucosylating has been identified.
- The discovery expands the known targets of C. sordellii LT, offering new insights into its cytotoxic mechanisms.
- Understanding LT's interaction with Ral may reveal new therapeutic targets for C. sordellii infections.